1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recorder incorporating the recording head, and more particularly is directed to a block-driving technique for a full-multiple type ink jet recording head.
2. Related Background Art
An ink jet recorder forms ejection ink droplets in compliance with a variety of methods and adheres these onto materials to be recorded thereon such as record paper to produce characters thereon. Above all, the ink jet recorder which utilizes heat as an energy source for forming ejection ink droplets is adapted to include multiple nozzles of high density with ease so as to have an improved characteristic that images with high resolution and quality can be obtained with higher speed.
This type of ink jet recorder comprises a plurality of ink droplets forming means for ejecting ink droplets through an ejection outlet by applying heat energy to ink, that is to say, a plurality of ink droplets forming means having an electric/thermal transducer which generates heat through the supply of electrical current pulse to heat ink, a plurality of integrated circuits (driving IC) arranged in the same substrate and for driving the electric/thermal transducer, and a recording head for a line printer, in other words, a so-called full multiple type recording head in which the outlets are disposed across the entire width of the member to be recorded thereon. This full-multiple type recording head employs a so-called block driving method in which a plurality of blocks each including a predetermined number of electric/thermal transducers are formed to drive by time division, in order to reduce the amount of electric current flowing at the time of driving.
Incidentally, the ink jet recorder making use of heat energy produces bubbles in the ink through the activation of electric/thermal transducer and ejects the ink directly from the ink ejection outlet of the recording head by virtue of the pressure resulting from the bubbles to thereby carry out recording. Therefore, it is necessary to keep the ink constantly stable and ready to be ejected.
The fluctuation (so-called back wave) in the pressure caused by ejecting the ink through the activation of the electric/thermal transducers, now and then vibrates ink in the adjacent ink passages through a common ink chamber. When the electric/thermal transducers arranged in the adjacent ink passages are successively driven, the ejection becomes unstable due to the fluctuation in the pressure arising from the previously driven electric/thermal transducer, thus bringing about the change in the amount of ejection ink to thereby cause irregularity in depth of the recorded image. In addition, the more the number of bits (the number of electric/thermal transducers included in one block) which are simultaneously driven, or the shorter the distance from the ejection outlet to be driven, the more this fluctuation in the amount of the ejection ink based on the fluctuation in the ink pressure occurs. It is also greatly influenced by the configuration of the common ink chamber which communicates with the ejection outlet.
In order to solve these problems, all the electricity may be driven at the same time. However, the electric current flowing into one electric/thermal transducer is large as much as several 10 mA to several 100 mA, so that an enormous amount of the electric current is required during driving and it is unsuitable for miniaturizing the driving source and the recording heads. For this reason, as described above, there has been used the method in which a plurality of blocks each including a plurality of electric/thermal transducers are formed to drive by time division. Furthermore, in U.S. Pat. No. 4,578,678, there is provided an atmospheric exposure section for ink in a part of the recording head, to thereby diffuse fluctuation in the pressure inside the common ink chamber at the time of ejecting ink through the specified ejection outlet, thus preventing it from interfering with the other ink passages. This method has, however, disadvantages that a minute air dust is liable to enter through the atmospheric exposure section, defectiveness of the ink ejection is induced by changes in physical properties attributable to the vaporization of ink, and the fixing of ink impedes the ink ejection. In order to overcome these disadvantages, the apparatus becomes more complicated.
One of measures for minimizing the occurrence of the problems due to the interference is that the distance d from the rear section of the energy generating member to the rear section of the common ink chamber is maintained sufficiently long. On experiment, the distance d was set longer than 6.0 (mm) to minimize the interference. This method goes, however, against the demand of minimizing dimensions of the recording head and the recorder itself. Additionally, as Si substrates are expensive parts, enlargement of the recording head leads to the increase of the manufacturing cost. In order to prevent the interference, the timing for ink ejection through the ejection outlet of a block after ejecting ink through the ejection outlet of the adjacent block is set after the elapse of time enough for the meniscus to return to the normal condition without being convex or concave. However, this method goes against the demand of high speed recording. The lag in the ejection timing brings about steps in the recorded characters or images and deteriorates the quality level of recording.